The proposed research is designed to shed light on the psychophysiological bases of individual differences in infants' emotional expression and regulation, and to identify psychophysiological indices of vulnerability to the development of affective and/or other behavioral disorders in early childhood. In a previous study, it was found that infants of depressed mothers exhibit atypical patterns of frontal lobe electroencephalographic (EEG) activity, as compared to infants of non- depressed mothers. These findings are particularly interesting in light of research documenting the role of the frontal lobe in affect expression, and in adult depression. In the present application, a replication of these findings with an independent sample of mothers and infants is reported. The purpose of the proposed research is to further explore the nature and clinical significance of these findings. Specifically, the research is designed to examine the consistency of infants' patterns of frontal EEG across different situations, and to determine whether the relation between maternal depression and infant frontal EEG is mediated by the mother's behavior toward her infant, as measured in situations outside of the psychophysiology laboratory. In addition, the research is designed to determine the degree to which infants' patterns of frontal EEG are stable from infancy to toddlerhood, and whether changes over time in mothers' depressive symptoms influence stability. Finally, the extent to which measures of frontal EEG enhance our ability to predict infants' behavioral disturbances when the infants reach toddlerhood (30 months) will be examined. Participants will be 135 30-month-old infants and their mothers, who previously participated in psychophysiological (EEG) and behavioral testing when the infants were 14 months of age. At that time, 75 of the mothers reported elevated levels of depressive symptoms and 60 mothers reported very few or no depressive symptoms and no current or past major depressive episodes. Thirty-month-old infants and their mothers will participate in psychophysiological testing designed to measure frontal EEG and autonomic activity during baseline and emotion-eliciting conditions. Mothers and infants also will be observed outside the psychophysiological laboratory in situations designed to assess patterns of mother-infant interaction and infant mastery motivation. Infant behavioral measures will focus on the assessment of affective behavior, task persistence (attention and mastery motivation), and self-regulation. Maternal behavior will be examined in three parallel realms: affective behavior, maternal strategies for directing her infant's attention, and maternal strategies for facilitating self-regulation. Mother's and teacher's report of child problem behaviors also will be assessed.